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X-86 Family Microprocessors
Advanced Microprocessors The 8085 was a 8 bit microprocessor . The X-86 Family takes us in the world of 8 , 16 and 32 bit microprocessors ! X-86 Family Major Attributes of X-86 Family INTEL 8086 Architecture The CPU is divided into 2 parts : 1) Bus Interface Unit (BUI) 2) Execution Unit . Bus Interface Unit contains queue , segment registers , and instruction pointer . Extension Unit contains flag register , general purpose registers , stack pointer register , and other pointers , index registers . BIU : Queue : To speed up execution of program , BIU fetches 6 instructions ahead of time from memory and stores them for EU in the FIFO register , called queue . Segment Registers : 16 bit registers 1) Extra Segment (ES) 2) Code Segment (CS) 3) Stack Segment (SS) 4) Data Segment (DS) These registers are used to store 16 bit starting addresses of memory segment . Instruction Pointer (IP) : The Code Segment (CS) register holds 16 bit starting address of segment , from which BIU is fetching instruction code bytes . The IP register holds 16 bit address of next code byte within Code Segment . EU : Flag Register : Flag is a flipflop , which indicates some Condition . 8086 has 16 bit flags with 9 active flags . General Purpose Registers : 8086 has 8 general purpose registers , labelled as AH , AL , BH , BL , CH , CL , DH , DL . These registers can be used individually for temporary storage of 8 bit data . The AL register is called as Accumulator . These registers in certain pairs can be used as 16 bit registers . E.g. AH and AL , BH and BL , CH and CL , DH and DL . Stack Pointer : The 8086 allows us to set 64KB of memory as stack . the 16 bit starting address of stack is stored in stack pointer . Programming Model of X-86 Family The Active Flags are Ac , Vm , Rf , O NT , IOPL , O,D,I,T,S,Z,AC,P,CY .; from 0 to 18 . Locations 19 to 31 are reserved . Flags of 8086 The 9 Active Flags in 8086 are OF , DF , IF , TF , S,Z,AC,P,CY .; from 0 to 15 . X-86 Family 8086 : # 16 bit microprocessor , introduced in 1978 .Its ALU , internal registers can work with 16 binary bits at a time 16 bit data bus and 20 bit address bus . Thus , it has 1M Byte memory locations # The least significant 8 bits of address are passed on the same eight lines of data bus . (multiplexed bus) # Words are stored in two consecutive memory locations . # Supports multiplication and Division # 80186 is an improved version of 8086 . In addition to 16 bit CPU , it has programmable peripheral (I/O) devices integrated in same package . 80286 : # 16 bit microprocessor , introduced in 1982 . designed for multitasking / operating systems . # 16 bit data bus and 24 bit address bus . # In 1984 , IBM introduced PC/AT version (Personal Computer/Advanced Technology) version of its PC using 80286 . # 286 was having real and protected modes of operation . In real mode , the processor can address only 1 M Byte , whereas in protected mode , it can address 16 M Bytes of memory . # Anility to work upto 1 GByte of virtual memory and hardware multitasking # The program written for 8086 can run on 80286 , in real mode . 80386 : # 32 bit microprocessor , introduced in 1985 . # 80386 is a logical extension of 80286 . it is more pipelined . # The instruction set of 80386 is a superset of 80286 # It has 32 bit data bus and 32 bit address bus . It can address 4 GBytes memory . # The 386 can operate in one of the two modes . : 1) Paged mode 2) Non-paged mode . # In paged mode , The 386 switches the paging unit and then the segment unit . the paged mode allows memory pages of 4 kB each to be swapped in and out from Disk . In nonpaged mode It operates similar to 286 . 80486 : # 32 bit microprocessor , introduced in 1989 . # 32 bit address bus and 32 bit data bus . # Th 486 is a large integral circuit which contains a fast built-in math coprocessor , a memory management unit , and a 8 kbyte cach memory . # 80486 has DX and SX versions . # The 486 achieves its high speed operation from it's faster clock speed . internal pipeline lined architecture and the use of reduced instruction setcomputing RISC to speed up internal microcode . # 486 also has DX2 and DX4 versions with double and triple clock speed . 80586 (Pentium) : # 64 bit microprocessor , introduced in 1993 . # 64 bit data bus and 32 bit address bus . # It has a dual pipelined architecture , which lets the processor to take in more than one instruction at a time . # The addition of data and code cache on chip improves processing speed . # Branch prediction is a new computing technique , in which the pentium makes an educated guess about the address of the next instruction following a conditional instruction . This prevnts instruction cache from running dry . # 64 bit data bus .Thus it can perform data transfers twice as fast as a 32 bit data bus in earlier versions Types of Questions Category:Computer Science